The present invention generally relates to a video signal coding apparatus, a coding method used in the video signal coding apparatus and a video signal coding transmission system having the video signal coding apparatus. More particularly, the present invention is concerned with a control of a buffer memory provided in a video signal coding apparatus in which the buffer memory is controlled in asynchronism with a buffer memory provided in a video signal decoding apparatus. Furthermore, the present invention is related to a coding method used in such a video signal coding apparatus, and a video signal coding apparatus.
Generally, systems which encode a video signal at a high efficiency are classified into a system in which a buffer memory on the transmitter side operates in synchronism with a buffer memory on the receiver side, and a system in which the buffer memory on the transmitter side operates in asynchronism with that on the receiver side. In a synchronous control of buffer memories, a frame synchronizing signal (also referred to as a framing signal) and a clock signal are transmitted to the receiver side so that the buffers on the transmitter and receiver sides operate in synchronism with each other. The above-mentioned synchronous control of buffer memories can prevent the occurrence of a failure of the decoding operation, such as a receiver buffer overflow. On the other hand, an asynchronous control of buffer memories provides large degree of freedom in the design of the system configuration. However, in order to prevent the occurrence of a failure of the decoding operation, it is necessary to control the amount of information generated on the transmission side.